The invention relates to a device for setting two-part fasteners, in particular blind rivets in which for setting a first part has to be pulled while a second part is held up, with a housing, a feed appliance on the housing to transfer a fastener into the housing through an orifice in the housing, an abutment which holds the second part during the setting process and a pulling device for pulling the first part during the setting process, the pulling device having a gripper at an open end of a pulling element which cooperates with a pulling piston which is movable forwards and backwards along an axis of the housing in a first chamber, wherein the pulling element opens the orifice to transfer a fastener.
Devices for setting two-part fasteners, in particular blind rivets, in which for setting a first part has to be pulled and a second part held, which devices have a housing, an abutment which holds the second part during the setting process, and a pulling device for pulling the first part during the setting process, which has a gripper at an open end of a pulling element which cooperates with a pulling piston which is movable forwards and backwards along an axis of the housing in the first chamber, are known. A device of this kind is described, for example, by EP 0 468 717. The feed of a two-part fastener is carried out manually in this device. Putting individual fasteners on to a device of this kind is relatively time-consuming. The use of a device of this kind is particularly disadvantageous for serial manufacture of products.
This problem has already been recognised. U.S. Pat. No. 4,628,722 describes a device for setting two-part fasteners, in particular blind rivets, in which for setting a first part has to be pulled and a second part held. The device has a housing and a feed appliance on the housing to transfer a fastener into the housing through an orifice in the housing. To achieve transfer of the fastener the pulling element has to be pulled back out of a setting position far enough to open the orifice.
The device has two pistons arranged behind one another, a pushing piston and a pulling piston, which are movable forwards and backwards along an axis in a common cylinder. The pushing piston is connected to a cylindrical pushing member. The pulling piston is connected to a cylindrical pulling element. The pulling element extends into the pushing member.
To set a fastener a pressure medium is introduced between the pushing piston and the pulling piston, so the two pistons move away from one another in opposing directions inside the cylinder. The pushing member herein exerts a pressure on the second part of the fastener, while the pulling element pulls on the first part of the fastener. After setting of the fastener has been carried out, a new fastener is put on the device.
For this purpose the pushing piston is impinged with a pressure medium, the pressure medium flowing out of the cylinder between the pistons, so the pushing piston is brought to rest against the pulling piston and the two pistons are driven into a final position in which the orifice is opened for the transfer of a fastener.
To position the two pistons for a further setting process the part of the chamber adjoining the pulling piston is put under pressure while the fluid with which the pushing piston has been impinged is pressed out of the cylinder by the movement of the two pistons. Once the two pistons have taken up a defined position inside the cylinder, the pressure medium is introduced between the pushing piston and the pulling piston, wherein the fluid acting on the pulling piston flows out of the part of the chamber adjoining the pulling piston.
Based on this, the object of the present invention is to develop further the known device for setting two-part fasteners, in particular blind rivets, in such a way that it is more simply designed in construction.
The device according to the invention for setting two-part fasteners, in particular blind rivets, in which for setting a first part has to be pulled and a second part held, has a housing and a feed appliance arranged on the housing by which a fastener is transferred into the housing through an orifice in the housing. The device further has an abutment, which holds the second part of the fastener during the setting process and a pulling device pulling the first part of the fastener during the setting process, the pulling device having a gripper at an open end of a pulling element, which cooperates with a pulling piston which is movable forwards and backwards along an axis of the housing in a first chamber by means of an actuating unit, the pulling element opening the orifice for the transfer of a fastener. The device according to the invention is characterised in that the pulling element extends through the setting piston and the pulling piston and the pulling element are movable relative to one another along the axis, the pulling element has a piston at the end opposed to the pulling device, a second chamber with variable volume is provided, limited by a casing, the piston and the pulling piston, and a third chamber with variable volume is provided, limited by a wall and the piston. A compressible medium is provided in both the second and the third chamber with variable volume.
By means of this configuration of the device according to the invention it is achieved that it is more simply designed in construction. The device also enables easier assembly thereof, as relatively few parts are necessary to produce the device.
Reduction of the components of the device also brings an improved ability to handle the device, if it is a hand-actuated device. The ability to handle the device is also improved by the fact that the device is relatively light, so the person operating the device is prevented from becoming tired while using it.
During the setting process the pulling piston is displaced away from the abutment along the axis of the housing in the first chamber. Displacement of the setting piston is carried out by means of an actuating unit. The path by which the pulling piston is displaced in the direction of the second chamber with variable volume preferably corresponds to the path which is necessary for performing the actual setting process. With the movement of the pulling piston the pulling element, which has gripped the first part of the fastener with a gripper, exerts a tensile force on this first part. If this first part is a mandrel shank of a blind rivet, the pulling piston, and thus also the pulling element, is pulled in the direction of the second chamber with variable volume for sufficient time for the mandrel shank to break.
A further process follows the actual setting process, in which the pulling element is moved away from the abutment inside the housing sufficiently for the pulling element to open the orifice, through which a further fastener can be loaded into the housing. This opening is achieved in the device according to the invention as follows: during the setting process there is a compression of the medium present in the second chamber with variable volume, so the pressure inside the second chamber rises. This rise in pressure effects an increasing axially directed force on the piston, the direction of which corresponds to a tensile force, so the pulling element is further displaced axially. The volume of the third chamber is decreased because of the movement of the piston. This leads to a rise in pressure of the compressible medium present inside the third chamber. A force of pressure of the medium of the third chamber acts on the front face of the piston opposed to the pulling piston. This force of pressure is opposed to the force of pressure of the medium of the second chamber.
The piston can be axially displaced by the force of pressure of the medium of the second chamber until a balance of forces of the forces of pressure applied to the piston occurs. This is preferably the case when the orifice has been opened by the pulling element.
According to an advantageous design of the device it is proposed that the pulling element takes up a final position in which the orifice has been opened by the pulling element, which is determined by a buffer cooperating with the pulling element. With a configuration of the device of this kind it is not necessary to stop a balance of forces of pressure from occurring on the piston. It is therefore not absolutely necessary to adjust the geometry of the piston and/or the pressures prevailing in the chambers in such a way that a balance of forces prevails in the final position. It must, however, be ensured that a balance of forces does not occur before the pulling element has taken up its final position.
When the pulling piston is opened, there is a relaxation of pressure of the compressed media present in the second chamber, which effects a movement of the piston and thus also of the pulling element into the initial position. This movement takes set relatively quickly. The configuration according to the invention also has the advantage that there is no need for additional connections for compressed air or such-like, which are necessary with conventional devices to move the pulling element into the setting position. Independence of such connections is also achieved.
Based on the configuration of the device according to the invention the actuating unit is only required to produce a sufficient tensile force during the setting process.
The medium present by compression in the second chamber is used to open the orifice, through which a further fastener is loaded into the housing. To obtain a movement of the piston with the pulling element by means of the pressure of the medium present in the second chamber in the direction of the third chamber, it is proposed, according to an advantageous further development of the device according to the invention, that the diameter of the piston is greater than the diameter of the pulling element, so a substantially annular face is available as pressure face.
According to yet another further development of the device it is proposed that the diameter of the piston is smaller than the diameter of the setting piston.
The path which the pulling element covers, caused by the pressure prevailing in the second chamber, is dependent on, among other things, the volume of the third chamber. It is therefore proposed that the third chamber is formed by a partial chamber with variable volume and at least one partial chamber, fluidically connected to the partial chamber with variable volume, which has a constant volume of the chamber. In this way a relatively large volume is created, so the rise in pressure in the third chamber is relatively slight. A relatively large displacement path of the pulling element can be achieved with a relatively slight rise in pressure. This configuration of the device also has the advantage that the at least one partial chamber can be arranged in such a way that it is positioned in a region of the device in which the partial chamber does not interfere with the handling of the device. In particular it is also hereby achieved that two-part fasteners can also be set by the device in regions with edges in proximity to which a face normal of a workpiece wall bisects the longitudinal axis of the device at an angle, for example a right angle.
According to yet another advantageous configuration of the device it is proposed that the partial chamber with the constant volume of the chamber surrounds the partial chamber with the variable volume of the chamber. A further development of the device of this kind also has the advantage of achieving a relatively compact construction of the device.
According to yet another advantageous further development of the device it is proposed that the partial chambers are designed as substantially cylindrical, preferably the partial chambers are arranged concentrically to one another. The partial chambers can, for example, herein be designed in a cast part, in particular an injection-moulded part.
According to yet another advantageous development of the invention it is proposed that the partial chamber with variable volume is connected by at least one channel to the partial chamber which has a constant volume of the chamber, the at least one channel having at least one portion with a raised flow resistance. This further development of the device has the advantage that during the movement of the piston the medium does not overflow out of the partial chamber with variable volume into the chamber with a constant volume of the chamber all of a sudden, but slowly.
This has the advantage that, for example if the device is used for setting blind rivets, the energy of the pulling element and the piston released when the mandrel shank of the blind rivet breaks is partially converted into a task of compressing the medium in the partial chamber with variable volume, so the piston and the pulling element are cushioned by the medium present in the other partial chamber, a return kick of the piston and the pulling element being prevented by the over-flowing of the medium out of the first partial chamber into the second partial chamber.
The portion which forms an increased flow resistance can preferably be achieved by arranging a choke in the channel.
According to a further advantageous development of the device it is proposed that the portion is formed by a check valve. This design of the device enables a pressure to be set in the partial chambers, so the piston and therefore also the pulling element can be stopped depending on whether the check valve is closed.
According to yet another advantageous configuration of the device it is proposed that the partial chamber with variable volume is fluidically connected to the at least one partial chamber with a constant volume in such a way that the flow resistance for a flow out of the partial chamber with variable volume into the partial chamber with constant volume of the chamber is greater than for a flow out of the partial chamber with the constant volume of the chamber into the partial chamber with the variable volume. In other words, by means of this advantageous design of the invention it is achieved that the speed of the flow of a medium out of the chamber with the constant volume of the chamber is to be greater than the speed of the flow out of the partial chamber with variable volume into the partial chamber with the constant volume of the chamber. This configuration of the device has the advantage that on the one hand a slowing down of the piston and therefore of the pulling element during a movement into the final position is achieved and on the other hand the piston and the pulling element can be moved out of this final position into a setting position relatively quickly.
If the geometrical measurements of the chambers and the piston remain the same, the travel path of the pulling element is dependent on the difference in pressure of the media in the second and the third partial chamber. To set the displacement path of the pulling element it is therefore proposed that the second chamber and/or the third chamber has at least one valve through which a medium can be introduced into the second and third chamber.
This further development of the device also has the advantage that if there are leakages, (connected) to a loss of pressure in the second and/or third chamber, these can be balanced out by external sources of pressure which can be connected to the at least one valve. The provision of at least one valve in the second and/or third chamber also has the advantage that the device can be quasi biased in the second and third chamber by corresponding impingement of pressure, thus enabling pre-determined courses of movement of the pulling element.
According to yet another advantageous configuration of the device it is proposed that the second and the third chamber are connected by at least one valve in such a way that the medium can flow out of the third chamber into the second chamber when the pressure in the third chamber exceeds a pre-determined pressure value. This configuration is particularly advantageous if the seal between the second and the third chamber enables an overflow of the medium out of the second into the third chamber. By recycling the medium out of the third into the second chamber an equal volume of the medium is always guaranteed in the third chamber.
To convert this idea it is proposed that at least one valve is provided in the form of a check valve. Instead of a check valve the valve can also be provided in the form of a safety valve, which can be actuated, for example, electrically and/or magnetically.
The second and the third chamber are preferably filled with the same compressible medium, so certain leakages between the second and the third chamber are, to a certain extent, not felt to interfere. Such leakages can arise in devices which are used in particular for series production, after a plurality of movements of the pulling element and thus of the piston.
According to yet another advantageous further development of the device it is proposed that the actuating unit by which the pulling piston is moved is a unit operated by an electric motor. If necessary gears can be provided between the unit operated by an electric motor and the pulling piston.
According to yet another advantageous configuration of the device it is proposed that the actuating unit is a unit which acts hydraulically, wherein by this a medium under pressure can be introduced into it through at least one passage ending in the first chamber, so the pressure medium can act on the side of the pulling piston remote from the piston. The pressure medium is preferably a fluid, in particular an oil.
Further advantages and details of the invention are explained with reference to the embodiments illustrated in the drawings.